Polyetherimide compositions and processes for production

ABSTRACT

Improved polyetherimide compositions and processes for their production are described. Various polyetherimide derivatives including water-soluble and tri-functionalisocyanate cross-linked resins are described. They permit production of water-based enamels and coatable particulates which may be employed in, for example, formulation of insulated electrical conductors.

This is a division of application Ser. No. 190,030, filed Sept. 23,1980, and now abandoned.

BACKGROUND OF THE INVENTION

Polyetherimide resins such as those described in U.S. Pat. No. 3,847,867have become increasingly important. These resins may be produced inknown manner by reaction between aromatic bis(ether anhydrides) andorganic diamines. They, and various derivatives, possess highlydesirable physical and electrical properties.

One of the most important classes of derivatives involves resinsproduced in part from polyisocyanate compounds. In these resins, thepolyisocyanate compounds may be employed in forming either or both ofthe polymer backbone and side chains. Most commonly, they represent across-linking agent for the resins.

In U.S. Pat. No. 3,541,038, for example, high molecular weightpolyimidamide resins are produced by condensation of tribasic acidanhydride with diisocyanate compounds. The resultant resins areespecially useful for coil-impregnation or electrical insulation. Toughfilms can also be produced from solutions of them.

Such polyisocyanate compounds, preferably employed in blocked form, arealso described in U.S. patent application Ser. No. 53,317, filed June29, 1979, where they are reacted to cross-link various polyetherimides.The resultant products have a veriety of specialized uses in, forexample, enamels for electrical insulation, laminate binders and hightemperature paints. Many general and additional uses are also known orapparent.

While the foregoing resins are satisfactory for many uses, furtherimprovements are desired. Better performance, new uses and additionalapplication or production techniques would enable substantialadvancement in their pertinent art or arts.

DESCRIPTION OF THE INVENTION

This invention involves improved polyetherimide resins and processes fortheir production.

According to one embodiment of this invention, there are providedwater-soluble polyetherimide resins. Such resins are derived by cleavageof polyetherimide polymer in the presence of amine.

Suitable polymer from which these water-soluble resins are produced maybe obtained commercially or produced by conventional means. For example,the polyetherimide polymer may be produced by reaction of aromaticbis(ether anhydride) with organic diamine as described in the previouslymentioned U.S. Pat. No. 3,849,867. A preferred aromatic bis(etheranhydride), for example, is 2,2 bis[4-(3,4-dicarboxyphenoxy)phenyl]--propane dianhydride; preferreddiamines are aromatic diamines, such as phenylene diamine.

Cleavage is preformed by combination of the polymer with water in thepresence of an amine. The resultant reaction is permitted to proceed at,for example, ambient temperature until the desired water solubility isachieved.

For cleavage, at least 25 and preferably from 15 to 35% amine by weightof polyetherimide polymer is employed and at least 25% and preferablyfrom 50 to 90% water by weight of polymer.

The resultant cleaved or water-soluble polyetherimide resins are ofparticular importance in that they allow production of water-basedenamels. Such enamels may be substituted for other, and particularlyorganic solvent-based, enamels. Thus they may be employed for suchapplications as electrical insulation or wires or other conductors.

The aqueous compositions of cleaved polymer most preferably will contain20 to 70% by weight of resin solids.

In addition to other normal enamel components which may be present,these water-based enamels may contain organic and water-misciblesolvent. Such organic solvent can assist in solubilization of the resinand/or other enamel components.

Any desired degree of water in the enamel is readily achieved. Commonly,for example, the polymer is cleaved in a low boiling organic solventwhich is immiscible in water. After achieving the desired degree ofcleavage, the organic solvent may be selectively removed from the higherboiling water by vacuum distillation. Other conventional techniques ofsolvent removal such as liquid/liquid extraction or the like may,however, also be utilized to accomplish or obtain transfer of thecleaved polymer to a more aqueous solvent solution.

For use, the enamel, preferably after the addition of a trifunctionalisocyanate agent, is simply applied to the conductor to be insulated,dried and then heat-cured. This results in production of a solid,insulating wall of the polyetherimide resin about the conductor.

In accordance with another embodiment of this invention, similarinsulation is formed by electrostatically coating a conductor with solidresin particulates and then melt-curing the particulates into a solidwall.

These resin particulates may be formed from polyetherimide resins suchas those described above. Preferably, however, the resin employed ispolyetherimide polymer which has been cross-linked with tri-functionalisocyanate agent. There is no criticality as to this agent and one ofthe commercially available agents mentioned below is most convenientlyemployed. Preferably from 1 to 40, and more preferably from 5 to 20parts of isocyanate agent per 100 parts by weight of polyetherimideresin will be used.

To facilitate the cross-linking reaction, it is preferred to utilizeblocked agent. Such blocked polyisocyanates are well known in thepolyester art. The term "blocked" means that the polyisocyanate has beenreacted with a group that will split off at the temperature employedwith the polymeric etherimide. As polyisocyanate components there may bementioned the cyclic trimer of 2,4-tolylene diisocyanate; mixtures ofthe cyclic tricyanate; 4,4'-diphenyl 2,4,6-triisocyanato toluene, andthe like.

Typical compounds which can be used to block the isocyanate groupings,e.g., are phenol; meta-cresol; paracresol; ortho cresol and mixturesthereof; the xylenols, e.g., 2,6-dimethylphenol; 4-ethyl phenol,4-t-butylphenol; 2-butylphenol; 4-n-octyphenol; 4-isoctylphenol, etc.;monohydric alcohols, such as methyl alcohol; ethyl alcohol, n-propylalcohol, and the like, acetoacetic ester, hydroxyalkylcarbamic acid arylesters, e.g., hydroxyethylcarbamic acid phenylester, mercaptans, e.g.,2-mercaptobenzothiazole, methyl mercaptans, and the like.

Others include the cyclic trimer of 2,4-tolylene diisocyanate having theisocyanate groups blocked with tertiary butylalcohol or tertiary amylalcohol or dimethyl ethinyl carbinol or acetoacetic acid ester or phenolor cresylic acid or ε--caprolactam or 2-mercaptobenzothiazole, orsuccinimide or phthalimide or diphenyl amine or phenyl--β-naphthylamine,triphenyl methane triisocyanate having the isocyanate groups blockedwith phenol or mixed cresols or tertiary butyl alcohol or phthalalimide,1,3,3-pentanetriisocyanate having the isocyanate groups blocked withm-cresol, etc.

As specific examples of such blocked isocyanates there may also bementioned Mondur S, wherein the isocyanate groups of the reactionproduct of 3 moles of mixed 2,4- and 2,6-tolylene diisocyanate withtrimethylol propane are blocked be esterification with phenol and MondurSH, wherein the mixed cyclic trimers of 2,4- and 2,6-tolylenediisocyanates have the three free isocyanate groups blocked byesterification with phenol. At present Mondour SH is the preferredblocked polyisocyanate.

Cross-linking will proceed in conventional manner. Normally, however,elevated temperatures are utilized (particularly with blocked agent) toexpedite this reaction. Thus, temperatures of at least about 50° C.,more desirably from 150° to 250° C., for a period of 1 to 5 hours arepreferred. Under these conditions, not only cross-linking, but alsoremoval of the resin dispersant, may be achieved.

Particulate formation is accomplished by drying a solution of thepolyetherimide and then grinding the resulting solid(s) to the desiredsize under temperature conditions below its softening point.

The drying step of, for example, a methylene chloride solution may beaccomplished in any known manner. Generally, however, it is performed atsubatmospheric pressure, and desirably at below the melting point of thepolymer. Spray drying techniques are particularly effective. They meetthese objectives and produce a grandular product. Similarly, thesolution may conveniently be freeze-dried. Both these latter techniqueshave the further advantage of yielding solid product suitable tofacilitate the subsequent grinding step.

Grinding of the dried polymer must occur at a temperature below that atwhich the polymer melts or softens. Otherwise, the ground polymer willagglomerate. However, because the grinding operation itself may productheat, the polymer is normally maintained under cryogenic conditions. Agood grinding temperature of most cases is below 0° C.

In the grinding step, the solid polymer is ordinarily reduced toparticulates of mesh size below 300, preferably of from about 200 to 270mesh. This provides optimum particulates with which to coat a conductor.

To provide insulation for the conductor, these particulates are firstelectrostatically coated onto the conductor. Generally, a coating havinga thickness of about 1 mil, preferably from 2 to 5 mils is utilized. Thecoated conductor may then be heated to at least the softening, andpreferably the melting, point of the polymer. This allows the polymerparticulates to coalesce and flow into a solid insulating wall about theconductor.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a cross-sectional view of an insulated conductor of thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENTS AND EXAMPLES

In the figure, a magnet wire 10, has a conductor 11 (normally metallic)covered peripherally with an insulating wall layer 12 of tri-functionalisocyanate cross-linked polyetherimide polymer. Although the figureillustrates a conductor wire which is circular in cross-section, it willbe understood that square, rectangularly or other shaped conductors in,for example the form of flat stripes or foils may also be used withoutdeparting from the scope of this invention.

The wires are visually inspected for smoothness in the usual manner, andtested for flexural strength at 25 percent elongation, for heat shock at260° C. after having been stretched 20 percent, for burnout which is anindication of resistance to high temperature in the winding of a stalledmotor, for abrasion scrape and for repeat scrape which is important toresist stresses in high speed winding machines, and the like. Such testsare well known in the art and are described, for example, in U.S. Pat.Nos. 2,936,296, 3,297,785, 3,555,113, and 3,865,785. Specifically, theflexibility is determined by stretching the control electrical conductor25 percent of its original length and winding it about a stepped mandrelhaving diameters of one, two and three times the wire diameter, thesmallest mandrel diameter at which failure does not occur being taken asthe test point (GE Method E 18B4). Heat shock is measured byprestretching wire samples to elongation of 20 percent and winding thewire so stretched on a conical mandrel having a diameter ranging from0.7 to 10 times the diameter of the bare wire and having an apex angleof about 20°, removing the conical shaped coil of wire from the mandreland placing it in an air circulating oven at the indicated temperaturefor 1/2 hour and taking the arithmetical average of five coils measuredat the largest diameter at which cracking appears, this diameter beingexposed as the inside of the coil divided by the diameter of the wire(GE Method E 18H3). For cut through, two coated wires are placedhorizontally and at right angles to each other in a suitable jig with a2000 g weight centered on the wires at the cross-over point. Thetemperature of the assembly is raised at a constant rate of 5 degrees Cper minute until the two conductors come in contact tieh each otherwhich is detected by electrical circuitry. The temperature at which thisshort circuiting occurs is considered the cut through temperature (NEMAMethod 50.1.1). Abrasion single, also known as unilateral scrape uses aconstant load on 9 mil diameter piano wire, which is at right angles tothe coated wire, moving along the length of the wire into an increasinglever arm until the insulation is removed and the needle makes contactwith the conductor. The distance the weighted head travels, multipliedby the weight gives a numerical value for scrape resistance. Repeatedscrape abrasion resistance is done with a cylindrical surface of a 16mil diameter #11 needle which is moved back and forth a distance of 3/8inch at a right angle to the wire under a load of 700 g. The number ofcycles required to cause the needle to break through the film is therepeat scrape value. Burnout is carried out by standard methods and thevalue is expressed as the official figure of merit (OFM) (NEMA Method58.1.1). Solvent resistance is also carried out by standard procedures(NEMA Method 51.1.1.)

EXAMPLE 1

A suitable polyetherimide polymer for wall or layer 12 may be made fromthe following:

    ______________________________________                                        PART I                                                                        Ingredients          Amounts                                                  ______________________________________                                        2,2 bis [4-(3,4-dicarboxyphenoxy)                                                                  1 mole                                                   propane dianhydride                                                           m-phenylenediamine   1 mole                                                   Solvent                                                                               Ortho-dichlorobenzene - 50                                                                     to make 20%                                                  parts            solution                                                     Toluene - 50 parts                                                    ______________________________________                                    

The mixture of ingredients is stirred and heated to reflux for 5 hoursunder a nitrogen atmosphere. In the course of reaction, water forms andis removed by azeotropic distillation. Upon cooling, the reactionmixture is poured into methanol to isolate solid polymer as aprecipitate.

The polymer is then combined as follows:

    ______________________________________                                        PART II                                                                       Ingredients          Parts by Weight                                          ______________________________________                                        Polymer              902.1                                                    Phenol end-blocked trimerized                                                                       90.2                                                    toluene diisocyanate (Mondur SH)                                              Dibutyl Tin Dilaurate                                                                               7.6                                                     Solvent              10,000.0                                                 Methylene Chloride                                                            ______________________________________                                    

The resultant solution is then spray-dried and cryogenically ground atbelow 0° C. to a particle size of about 270 mesh. These particles arethen electrostatically coated onto conductor 11 and then heat-cured inplace to produce an insulated magnet wire 10.

EXAMPLE 2

Isolated polymer produced in accordance with Part I of Example 1 iscombined as follows:

    ______________________________________                                        Ingredients       Parts by Weight                                             ______________________________________                                        Polymer           400                                                         Dimethyl ethanol amine                                                                          100                                                         Water             100                                                         Solvent           1,000                                                       N--methyl pyrrolidine                                                         ______________________________________                                    

The resultant solution is maintained under agitation at ambienttemperature for about 4 hours until the desired degree of cleavage ofpolyetherimide is achieved. To this solution is added 354 parts of waterto produce a water-based enamel. This enamel is applied onto a metallicconductor in 6 passes using a 15-foot gas fired down-draft oven. Thereresults a magnet wire such as that shown in the figure and previouslydescribed.

EXAMPLE 3

Isolated polymer produced in accordance with Part I of Example 1 iscombined as follows:

    ______________________________________                                        Ingredients       Parts by Weight                                             ______________________________________                                        Polymer           800                                                         N--methylpyrrolidone                                                                            1147                                                        Dimethyl ethanolamine                                                                           200                                                         Water             100                                                         ______________________________________                                    

The mixture is stirred and heated to 130° C. for approximately 4 hoursuntil all the polymer is in solution. Then, at 90° C., 420 parts ofwater is slowly added. The viscosity at 25° C. is 570 centipoise; solidscontent 33.4%.

To 1000 parts of the above solution is added 81 parts of a 60%non-volatiles (N.V.) content solution of a phenol end-blocked trimerizedtoluenediisocyanate (Mondur SH) and 2.6 parts of dibutyltin dilaurate. Aclear solution suitable for use as an enamel in this invention isobtained.

The foregoing enamel is applied to #18 awg copper wire in a 15'gas-fired down-draft tower into seven passes at a temperature rangebetween 290° and 490° C. The wire test results are as follows:

    ______________________________________                                                         Coating speed (feet/minute)                                                   40       50                                                  ______________________________________                                        Build (coating thickness, mils)                                                                   3.0        3.0                                            Solvent resistance 50/50, 10 min.                                                                OK         OK                                              Flexibility 25%+   1×   1×                                        Cut through, 2000 g., °C.                                                                  341        371                                            260° C.% - 30'                                                                            1×   2×                                        Burnout, OFM       11.5       10.7                                            Abrasion-single    1600       1800                                            Repeat scrape       62         78                                             ______________________________________                                    

EXAMPLES 3-5

Wire enamels are prepared from the following:

    ______________________________________                                        Ingredients           Parts by Weight                                         ______________________________________                                        Polyimide polymer as in Example 1,                                                                   80                                                     Part I                                                                        N--methylpyrrolidone  1620                                                    Dimethyl ethanolamine 150                                                     ______________________________________                                    

The N-methylpyrrolidone and dimethylethanolamine are added to a flaskand heated with stirring to 125° C. The polyimide is slowly added andstirring is continued. The temperature is raised to 130° C. and held for6 hours. The mixture is then cooled to 100° C. and 764 g of water isadded. The viscosity at 25° C. is 277 cs; the solids content is 27% at200° C.

The solution as prepared is suitable for use as a wire enamel (Example3) according to this invention. Two additional embodiments are prepared:to 800 g of Example 3 enamel is added 81 g of KL5-7005 alkanol blockedisocyanate (40% solution, Mobay Company and the enamel is designatedExample 4; and to 800 g of Example 3 enamel is added 40 g of phenolblocked trimerized toluenediisocyanate (Mondur SH) and the enamel isdeisgnated Example 5.

The foregoing enamels are applied to #18 awg copper wire in a 15'gas-fired down-draft tower with seven passes at a temperature rangebetween 290° and 490° C. The wire test results are as follows:

    ______________________________________                                                          Example                                                                       3      4      5                                             ______________________________________                                        Coating speed (feet/min.)                                                                          30       30     30                                       Build (coating thickness, mils)                                                                   3.0       2.9    3.2                                      Solvent resistance 50/50 10 min.                                                                  OK       OK     OK                                        Flexibility 25%+    2× 2×                                                                             2×                                  Cut through, 2000 g, °C.                                                                    298      368    405                                      30't shock, 20% - 260°                                                                     2× 2×                                                                             2×                                  Burnout, OFM        8.5      12.9   12.5                                      Abrasion - single   1200     1300   1200                                      Repeat scrape        38       43     20                                       ______________________________________                                    

The foregoing results show that high quality coated magnet wires can beproduced following the teachings of the present disclosure.

To more completely describe the present invention, the disclosures ofthe various applications and patents mentioned above are incorporatedherein by reference. Obviously, many modifications and variations of thepresent invention are possible in the light of the above and otherwell-known teachings. It is therefore to be understood that changes maybe made in the particularly described embodiments of this invention. Allare within the full intended scope of the invention as defined in theappended claims.

We claim:
 1. A process for preparing a water soluble coatable resinmaterial comprising preparing a solution of polyetherimide polymer in asolvent therefor and mixing said solubilized polymer at ambienttemperature with sufficient water to obtain the desired final viscosityin the presence of from about 15% to about 35% amine by weight of thepolyetheramide solid resin material.
 2. The process of claim 1, whereinthe polymer is the reaction product of aromatic bis(ether anhydride)with organic diamine.
 3. The water soluble resin material prepared bythe process of claim
 1. 4. The resin material of claim 3, wherein thepolymer is the reaction product of aromatic bis(ether anhydride) withorganic diamine.
 5. The resin material of claim 3, wherein the solutionadditionally contains an organic solution of from about 1 to about 40parts of a blocked trimerized diisocyanate per 100 parts ofpolyetherimide resin.
 6. The resin material of claim 5 wherein theblocked trimerized diisocyanate is a phenol blocked trimerizedtoluenediisocyanate.